1. Field of the Invention
The present invention relates to a fryer mainly for business use, for heating cooking oil filling an oil tank.
2. Description of the Related Art
As a device for frying food such as fried potatoes, a fryer for business use has been heretofore used in which an outer wall of an oil tank is directly heated by a burner so as to increase a temperature of cooking oil (hereinafter, simply referred to as oil) in the oil tank. Such a fryer has a constitution as described below. For example, as shown in FIG. 5, an inclined surface 10a is formed on a side surface of an oil tank 10. The inclined surface 10a is inclined toward a bottom and the outer wall thereof is heated by a burner 31. A net 11 for placing a basket containing the food is disposed over this inclined surface 10a. Thereby, a cooking zone for frying is provided in an upper portion of the oil tank 10. In such a constitution, when the outer wall of the inclined surface 10a is heated by the burner 31, the temperature of the oil rises near the inclined surface 10a. Thus, the oil is convected in an intermediate zone provided at a heating position under the cooking zone. As a result, the temperature of the oil also gradually rises in the cooking zone in which the food is located. Meanwhile, the side surface of the oil tank 10 includes a vertical surface and the inclined surface 10a alone toward the bottom. Fry residues, which fall away from the food during the cooking and remain in the oil after the cooking, thus sink into a cold zone under the heating position in which a heat is difficult to transfer. The fry residues are therefore prevented from being carbonized. The contamination and deterioration of the oil are consequently suppressed.
In this fryer, the cooking zone is widely formed so that large quantities of food can be cooked at a time. Thus, the oil is heated in a lower portion of the cooking zone. Desirably, the shortest time possible is required for raising the oil temperature to a suitable temperature after the start of heating operation or the introduction of frozen food or the like. However, the raising of the oil temperature in the cooking zone to the suitable temperature requires the raising of the oil temperature in the intermediate zone as well. Thus, the rise in the temperature takes a longer time due to a great deal of oil. Moreover, the oil is disadvantageously prone to deteriorate because a great deal of oil also including the oil in the intermediate zone is heated to a high temperature.